Roosevelt Reservoir Reservoir Report

Last Updated: December 15, 2025

Roosevelt Reservoir, also known as Green Lake Reservoir, is a vital water resource located within Seattle City Limits in King County, Washington.


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Summary

Managed by the Washington Department of Ecology, this local government-owned reservoir was completed in 1910 for the primary purpose of water supply. With a maximum storage capacity of 181 acre-feet and a normal storage capacity of 153 acre-feet, the reservoir covers an area of 8.4 acres and serves as a crucial source of water for the surrounding area.

The dam at Roosevelt Reservoir is of Earth type, with a hydraulic height of 23 feet and a structural height of 23 feet. The reservoir has a high hazard potential but is currently in satisfactory condition, as assessed in April 2021. With a drainage area of 0.01 square miles and a maximum discharge of 45 cubic feet per second, the reservoir plays a key role in managing water resources in the region. Regular inspections are conducted every five years to ensure the safety and functionality of the dam, demonstrating a commitment to proper maintenance and risk management.

As a significant component of the water infrastructure in the area, Roosevelt Reservoir not only provides essential water supply but also contributes to the overall management of water resources in the region. With its strategic location and high hazard potential, the reservoir serves as a critical asset for the community and underscores the importance of effective regulation, inspection, and maintenance practices to ensure the safety and reliability of the water supply system in King County, Washington.

Year Completed

1910

Dam Length

1920

River Or Stream

Tr-Puget Sound-Offstream

Primary Dam Type

Earth

Surface Area

8.4

Hydraulic Height

23

Drainage Area

0.01

Nid Storage

181

Structural Height

23

Hazard Potential

High

Foundations

Soil

Nid Height

23
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.